1. Field of the Invention
The invention concerns hydraulic jacks containing more than two cylinders. In jacks of this type which contain, for example, two cylinders, one cylinder may be designated the "working cylinder" since it encloses a piston intended to apply a displacing force to a mobile structure, and the other may be designated a "master cylinder" since it encloses a piston that is connected mechanically or hydraulically with the piston of the "working cylinder". Jacks of this type are used in particular in a hydraulic circuit to impose synchronous strokes on all of the pistons of the "working cylinders". In fact, synchronization is necessary in all assemblies of mobile structures, wherein mutual connections have weak or zero rigidity and the hydraulic synchronization of the control cylinders makes it possible to avoid the complexities of a mechanical synchronizing system.
2. Brief Description of the Prior Art
Systems of multiple chamber hydraulic cylinders are already known, as shown in French Patent No. 2,433,661. They are primarily used to actuate the thrust reversers of turbojet engines. In order to provide these systems with minimum space requirements and maximum rigidity, each jack has double cylinders and is of the type comprising: a "working cylinder" in which a first piston is slidably retained, with a hollow cylindrical piston rod attached thereto and connected with the mobile structure to be controlled; and, a "master cylinder" formed inside the hollow piston rod and containing a second piston fixedly placed between two rigid conduits, one of which passes through a first chamber of the "master cylinder", the first piston and a first chamber of the "working cylinder", and the other passes through the second chamber of the "master cylinder" and the second annular chamber of the "working cylinder" surrounding the "master cylinder", which moves in said chamber simultaneously with the first piston separating the two chambers of the "working cylinder".
Each chamber of the "master cylinder" communicates through a passage in the second piston with the conduit attached to its opposing face. By these arrangements, the differential thrust applied to the second piston under the effect of the hydraulic pressures prevailing respectively in the two chambers which are separated by the second piston is transmitted to the first piston connected with the rod of the jack.
It will be seen hereinafter in the course of the present description, why this configuration of the prior art has certain disadvantages, notably the fragility of certain elements, a large longitudinal dimension, and the necessary complexity of the connections to be established between the rod of the jack and the structure to be moved.